Brazil football legend Pele is in Denmark to boost Rio's bid hopes
Rio de Janeiro's 2016 Olympic bid team have lodged a complaint against rivals Madrid after a Spanish Olympic official criticised the city's credentials.
The Brazilian city was labelled as "the worst of the four candidates" by Spain's Olympic vice-president Jose Maria Odriozola.
The Madrid bid team have swiftly apologised for Odriozola's comments.
Chicago, Madrid, Rio and Tokyo are fighting it out, with the decision to be announced in Copenhagen on Friday.
The row is likely to heighten the tension between the four rivals as the International Olympic Committee (IOC) prepares to reveal its decision.
Odriozola also highlighted the Brazilian city's security issues as well as dismissing its marketing strategy to host "the first South American Games".
His comments prompted organisers of Rio's bid to officially complain to the IOC's ethics committee.
"We are disappointed at these comments which don't correspond with the conclusions of the IOC's evaluation commission," said a Rio spokesman.
While Odriozola insisted his comments were his own and did not reflect the official bid, Madrid 2016 chief executive Mercedes Coghen was forced to apologise for to their Brazilian counterparts.
"Whatever happened, we want to apologise to Rio," said Coghen.
"We believe that all four bids are very good bids. We have tried throughout to have fair play.
"I believe all four cities are very, very good cities. All four can win this race but hopefully Madrid will be the winner."
The complaint is Rio's second to the IOC ethics committee this week following remarks from Chicago mayor Richard M Daley, who said that hosting the 2014 football World Cup was not the same as hosting the Games.
Under IOC rules, host cities are not allowed to criticise each other's bids.